Which term of the series `21, 15, 9, ...` is `-39` ?

Which term of the series : 21, 18, 15, is -81 ? Can any term this series be zero ? If yes, find the number of terms.

Which term of the AP : 21, 18, 15, ..... is - 81 ? Also ,is any term 0 ? Give reason for your answer .

Which term of the AP: 21,18,15, is 0?

Which term of the AP : 21, 18, 15,... is - 81 ? Also, is any term 0? Give reason for your answer.

Which term of the AP:- 21, 18, 15, . . . is – 78?

The nth term of the series 3+7+13+21+... is

Which term of the AP : 21, 18, 15, ... Is -81?Also, is any term 07 Give reason for your answer.

Which term of the AP 21, 18, 15, … is -81?

Which term of the AP 21, 18, 15,… is zero?